Method and apparatus for surveying the direction and inclination of a borehole

ABSTRACT

A magnetic reference member is maintained in a stationary position within a drill during drilling operations. The reference member is released in response to temporary cessation of the drilling operations and then seeks a predetermined reference orientation. In response to resumption of drilling operations, the reference member is again clamped in a stationary position and the relative position of the drill with respect to the reference member is detected and transmitted uphole during the drilling operations.

United States Patent Inventor Jan J. Arps Dallas, Tex. 837,700

June 30, 1969 Nov. 23, 1971 Arps Corporation Dallas, Tex.

Appl. No. Filed Patented Assignee Primary Examiner-Rodney D. Bennett,Jr. Assistant Examiner-H. A. Birmiel Attorney-Richards, Harris & Hubbard24 Claims, 12 Drawing Figs.

H 340 18 ABSTRACT: A magnetic reference member is maintained in a U.S.C1sationary position within a drill during drilling oPermions- Thereference member is released in response to temporary Int. Cl GO 1 4dcessation of the drilling operations and then seeks a predate: h g lmined reference orientation. In response to resumption of Field of Searc3 I20 drilling operations, the reference member is again clamped in24/48 340/18 a stationary position and the relative position of thedrill with respect to the reference member is detected and transmitteduphole during the drilling operations.

a le b semi #54 64 a; 76 4 A 5 -//2 asa 102 i 82 84 l %uo \kT 33 .s .106

earl 96 9O SHE 1 0H1 47 TIME PUTER E R U S S E R P W P PATENTEmnv 2 31911 I COM IZ IIX [Z 30 HOLE DRIFT FIG.4

PATENTEIJIIII'I 23 Ian 3,622 971 SHEET U F 4 I56 ANALOG |NPUT(FROM I) A7 D 6 LADDER POWER-ON CONVERTERS NETWORK RESET(FROM I44) COMPARATOR I74LCl C K 4 I84 3 V (FROM INTERFACE 2 I78) I Q'?Z I80 TO 2 I (I44) I82 FI88 I90 INTER FACE 186 I25 MSEc.

POWER-ON RE S E T PULSE SOLENOID FIG. II

W F 236 INVENTOR- PULSE D JAN J. ARPS SOLENOID V DRIVER FIG/2 $4 z/g y ZATTORNEYS FIELD OF THE INVENTION This invention relates to the surveyingof boreholes, and more particularly to the automatic intermittentsurveying of the inclination and direction of a borehole during nonnaldrilling operations.

THE PRIOR ART the drilling apparatus to prevent an excessively crooked.

borehole. Additionally, in deeper offshore oil well drilling areaswherein fixed platforms are extremely expensive, it is thus economicalto build a central platform and to complete a number of developmentwells from the central platform by means of directional drilling. Insuch directional drilling, it is important to maintain the borehole ator near the desired direction and angle.

A number of techniques have been heretofore developed for intermittentlyproviding indications of the inclination and direction of a borehole.For instance, the McLaughlin et al. U.S. Pat. No. l,987,696 and theTrotter et al. U.S. Pat. No. 2,508,899, among others, disclose freelymovable spherical magnetic members disposed adjacent the drill bit, withstructure provided for clamping the magnetic member at a selected timeso that the entire drill string may be removed from the borehole toenable detection of the relative position of the magnetic member and thedrill bit. This periodic interruption of drilling operations formeasurement of the angle and direction of the drift of the borehole istime consuming and economically undesirable. Other conventionalsurveying techniques are also objectionable in that they involveinterrupting the drilling operation, running a surveying instrument on awire or cable down the drill string, taking a reading and thenretrieving the instrument. Such interruptions may require up to 35percent of the total drilling time.

SUMMARY OF THE INVENTION In accordance with the present invention, areference member is maintained in a stationary position within a drillduring the drilling operations. The reference member is released inresponse to cessation of the drilling operations and then seeks apredetermined reference orientation. The reference member is clamped ina stationary position in response to resumption of drilling operations,and then the relative position of the drill with respect to thereference member is automatically detected during drilling operationsand telemetered uphole.

In accordance with a more specific aspect of the invention, a generallyspherical magnetic reference member is disposed within a chamber in theregion of a drill bit. Structure responsive to mudflow in the drillsystem is provided to clamp the reference member in a stationaryposition during drilling operations, and to release the reference memberfor free movement during cessation of drilling operations. The relativepositions of the reference member and the drill bit are detected duringdrilling operations and indications of the relative positions aretelemetered uphole by variances in mud pressure.

In accordance with another aspect of the invention, a sphericalreference member is freely mounted within a drill. Structure is providedfor selectively clamping the reference member and for contacting contactpoints disposed on the reference member. A multiplexor sequentiallysenses the position of the contact points. An analog-to-digitalconverter is responsive to the multiplexor to generate digital signalsrepresentative of the position of the contact points. A control logiccircuit is operable in response to the converter for controlling amudflow valve in the drill to telemeter ses uphole.

pressure pul- THE DRAWINGS For a more complete understanding of thepresent invention and for other objects and advantages thereof,reference is now made to the following description taken in conjunctionwith the accompanying drawings, in which:

FIG. I is a somewhat diagrammatic illustration of a typical directionaldrilling system;

FIG. 2 is a partially sectioned view of the drilling system shown inFIG. 1 illustrating the present invention;

FIG. 3 is a sectional view of a portion of the invention shown in FIG.2;

FIG. 4 is a diagrammatic illustration of the geometry of the compasssphere and'latitude rings'of the invention;

FIG. 5 is an illustration of pump pressure telemetry according to theinvention;

FIG. 6 is a schematic diagram of the electrical connections between oneposition of the compass sphere and the sensing device of the invention;

FIG. 7 is a block diagram of the position-sensing circuitry of theinvention;

FIG. -h are sample timing waveforms for the operation of portions of thesystem shown in FIG. 7;

FIG. 9 is a schematic diagram of the (SO-channel multiplexor oftheinvention;

FIG. 10 is a block diagram of the eight-level analog-todigital converterof the invention;

FIG. II is a block diagram of the control logic circuitry shown in FIG.7; and

FIG. 12 is a block diagram of the solenoid driver shown in FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. I, aconventional oil derrick generally designated by numeral 10 is disposedover a borehole 12. A drill string 14 extends through the borehole l2and terminates at a conventional drill bit 16 at the bottom of theborehole. The upper end of the drill pipe is attached to and supportedby a kelly 18 which is rotated by a rotary table 20 operated by drawworks 22 in the conventional manner. The traveling block 24 supports aconventional swivel and hook attached to the drill string 14. A drillingfluid conduit 26 receives drilling fluid from a pump 28 which dischargesdrilling fluid from a supply sump 30 into the drill string 14 in theconventional manner.

A pressure change detecting device 32 is connected in the drilling fluidconduit 26 for generation of electrical signals representative ofpressure changes in the drilling fluid supply. These electrical signalsare fed through an amplifier 34 to a conventional recorder 36.Additionally, the signals are fed to a computer system 38. The apparatusthus described, and particularly the detecting device 32, amplifier 34and recorder 36, may be of the type described in U.S. Pat. No. 2,930,137issued on Mar. 29, 1962, to .l. J. Arps, or any other conventional typeof system.

A nonmagnetic drill collar structure 40 is connected above the drill bit16 to detect the direction of inclination of the drill stringI4.according to the invention. The drill collar 40 is constructed fromnonmagnetic material, such as K-Monel, to allow the use ofmagneticmembers within the collar.

FIG. 2 is a partially sectioned view of the drill bit 16 and the drillcollar 40 and illustrates a surveying instrument 42 centrally locatedwithin an annular mudflow opening 44 through the drill string 14. Themudflow through the aperture 44 thus flows downwardly through theannular space between the instrument 42 and the drill collar 40. The mudthen flows through a pulsation valve 46 and passes outwardly from thedrill bit 16 through bit nozzles 48 in the conventional manner. Themudflow then travels upwardly through the annular space between mean"collar 40 and the borehole wall. The pulsation valve 46 is adapted whenclosed to throttle or restrict the downward flow of the drilling mudthrough the drill string and thus create a pressure change signal in themud which is sensed by the device 32. This pulsation valve may be of anyconventional type, or of the type disclosed in the previously identifiedUS. Pat. No. 2,930,137.

The surveying instrument 42 of the invention includes a spinner cap 50,preferably constructed from a suitable material such as hard rubber, andequipped with spiral vanes which cause the cap to rotate due to thedownward mudflow. The rotating shaft, not shown, of the mud-drivenspinner cap 50 is connected through a stuffing box to a constant voltageelectric generator 52 which provides electrical power for the instrument 42. Alternatively, a battery may be utilized for a voltage supply.The inclination-surveying apparatus of the invention is contained withinan intermediate section 54. The lowermost section 56 of the assemblycontains electronic instrumentation and switching mechanisms whichperiodically actuate the valve 46 in a manner to be subsequentlydescribed in greater detail.

FIG. 3 illustrates in detail a cross section of the intermediate section54. Upstream mud pressure inlet channels 60a-b provide communicationbetween the annular mudflow opening 44 and an aperture 62 which opensinto a spring-loaded bellows 64. Differences in fluid pressure withinthe inlet channels 60a-b cause bellows 64 to constrict or expandvertically. Downstream mud pressure inlet channels 66ab communicatedirectly with a second bellows 68 which also expands or constrictsvertically in accordance with the fluid pressure within the inlets 66ab.A chamber 70 is formed between bellows 64 and 68, with a smallersecondary chamber 72 communicating with chamber 70 by apertures 74.Chambers 70 and 72 are filled with a suitable highviscosity oil orglycerin which provides damping action to the position-sensing mechanismwithin the chamber 70.

Bellows 64 is connected at its lower end to a gripping device 76 whichslidably receives the enlarged end ofa shaft member 78. A spring 80 isdisposed within the gripping device 76 and provides a constant downwardbias on the enlarged end of the shaft 78. Spring 80 is provided toprevent the pressure within the chamber 70 from becoming excessive andthereby possibly damaging the sensing structure therein. The shaft 78 isintegrally connected to a constraining member 82 which includes asemispherical concave surface 84 in the lower end thereof. Apertures86a-b enable the damping liquid to circulate freely through theconstraining member 82. The constraining member 82 is dimensioned tomove freely axially within the chamber 70, but also such that the member82 is maintained in an aligned position with respect to the axis of thedrill collar and the borehole.

A compass sphere 90 is pivotally mounted on a pivot member 92 which isrigidly connected to the flange 94 which divides chamber 70 and chamber72. The compass sphere 90 is constructed from relatively light,nonmagnetic material and includes a cone-shaped opening 96 cut into thebottom portion thereof, so that the pivot member 92 may be connected tothe center of the compass sphere 90. A low-friction bearing 97 isprovided between the pivot member 92 and the compass sphere 90, thebearing 97 also serving as an electric contact between the sphere 90 andthe pivot member 92. An annular ballasting or weighted portion 98 isprovided on the compass sphere to bring the center of gravity of thecompass sphere below the low-friction bearing 97. A bar magnet 100 isdisposed within the compass sphere 90 and thus tends to main tain thecompass sphere 90 in a horizontal position and oriented toward magneticnorth. The cone-shaped opening 96 allows a substantial amount of freedomof movement of the sphere 90.

The compass sphere 90 is further provided with three spaced-apartelectrical contact points T, N and E on its outer periphery. Contactpoints T, N and E preferably comprise small circles of electricallyconducting material such as copper or the like. Contact point T isdisposed at the exact top center of the compass sphere 90, contact pointN is removed 30 from the contact point T in the direction towards thenorth pole of the magnet 100, and contact point B is removed 30 in aneasterly direction from the top of the sphere. Contact points T, N and Eare electrically connected through resistors 102, 104 and 106. Theterminals of each of the resistances 102, 104 and 106 are commonly tiedto the electrically conductive bearing 97. A predetermined voltage isapplied to the pivot member 92 to provide voltage to each of theresistors 102,104 and 106.

The magnitudes of each of the resistors 102-106 are different, and inthe preferred embodiment, resistance 102 is 50,000 ohms, resistance 104is l00,000 ohms and resistance 106 is 200,000 ohms. It will, of course,be understood that various other magnitudes may be utilized for theresistors to provide various required operating characteristics for thesystem. The relative magnitudes of the resistors enables the electroniccircuitry in unit 52 to detect the relative position of the compasssphere 90.

The concave surface 84 of the constraining member 82 is provided with aplurality of concentric metallic latitude rings 110. As will be laterdescribed, in the preferred embodiment 60 rings are concentricallydisposed on member 82. Each of the rings 110 are individually connectedto one of a plurality of electric wires 112, each of the wires 112 beingbrought together in a bundle 114 which is connected to the scanningcircuitry in the electronic unit 52. Each metallic part in the assemblyshown in FIG. 3 is made from a nonmagnetic material, except the magnetwhich comprises a strong permanently magnetized material.

in operation of the device shown in FIGS. l3, when mud is flowingthrough the annular opening 44 during normal drilling, a higher pressureis provided opposite the upstream inlet channels 60a-b than adjacent thedownhole inlet channels 66a-b. The pressure differential thus causes thetop bellows 64 to be downwardly extended and the bottom bellows 68 to bedownwardly constricted. The downward movement of the top bellows 64moves the constraining member 82 downwardly to clamp the compass sphere90 firmly against the bearing 97.

When the constraining member 82 clamps the compass sphere 90 in astationary position, the three electrical contact points T, N and E onsphere 90 make electrical contact with certain of the concentriclatitude rings on the member 82. The electrical scanning circuitry inunit 52 senses the position of the compass sphere 90 by determiningwhich of the concentric rings 1 10 contacts the electrical contacts ofthe sphere 90. The electronic unit 52 then modulates the pressurepulsation valve 46. The modulation, or temporary partial closure, of thevalve 46 causes momentary pressure spikes in the mud stream which may bedetected at the surface to denote the angle and the direction of slopeof the drill string in a manner to be subsequently described.

Whenever a new joint of drill pipe is to be added to the drill string,the driller stops the rotary table and lifts the drill string until thestring can be secured by slips in the rotary table. The driller thenstops the mud pumps and the mud circulation, unscrews the kelly" fromthe top part of the drill string and moves the kelly aside. A new jointof drill string is then picked up and screwed on. The drill string isthen lowered by means of elevators," the kelly picked up, remounted andscrewed on and circulation of the mud and rotation of the drill stringis resumed.

While the new joint of drill pipe is being added, the absence of mudflowthrough the annular opening 44 causes the abovedescribed pressuredifferential between the inlet channels 60a-b and 66a-b to disappear.The spring-loaded bellows 64 is then moved upwardly and the grippingdevice 76 moves the shaft 78 and the constraining member 82 upwardly torelease the clamping action on the compass sphere 90.

When the compass sphere 90 is released from constraint by theconstraining member 82, the drill pipe is in a stationary condition. Thecompass sphere 90 will thus seek a position whereby the compass bar 100is in a horizontal position and is pointed to the magnetic north, suchthat the contact point T on the compass sphere 90 is in a verticalposition. The liquid within the chamber 70 is such that it retains asuitable high viscosity even under the relatively high temperatures of aborehole environment, and thus quick damping is provided to theoscillatory motions of the compass sphere 90 in seeking its stabilizedposition.

As long as there is no mud circulation, the compass sphere 90 remains inits unrestrained condition. After the new joint of drill pipe has beenadded, and while the kelly is remounted and screwed on, the compasssphere 90 will seek its final position which effectively measures theangle and direction of the drift of the borehole. The compass seeks itsfinal position in less time than is required to mount the kelly assemblyand screw the assembly into the last joint of drill pipe added. When mudcirculation is again resumed, the pressure differential ex erted betweenthe inlet chambers60a-b and 66a b causes the constraining member 82 toagain clamp the compass sphere 90 to preserve an accurate reading of theangle and direction of the borehole drift.

Resumption of the mudflow also reactivates the entire electronic unit 52by rotating the spinner cap 50 to provide electric powerfor theinstrumentation and telemetry operation of the device. The intelligencecontained in the position of the compass sphere 90 is then detected bythe concentric latitude rings I10, and the resulting information istranslated into a series of electrical pulses which activate pressurepulsation valve 46 in a time sequence representative of the position ofsphere 90.

FIG. 4 is a somewhat diagrammatic view of the top portion of the compasssphere 90 within a slanted borehole taken along the axis of theborehole, along with indications of the positions of the concentriclatitude rings 110 upon sphere 90 when member 82 restrains the sphere90. The point C thus represents the center of the concave surface 84 ofthe member 82, while the points T, N and E represent the electricalcontact points on the sphere 90. The angular distance between point Cand the contact point T represents the angle of the drift of theborehole. Also, the angular distance between C and N represents a pointin the magnetic meridian 30 northward from the vertical, while thedistance between point C and point E represents a point 30 eastward fromthe vertical.

In FIG. 4, the latitude rings ll0 disposed over the sphere 90 are shownat intervals of approximately but it will be understood that in actualpractice the contact rings will have a much closer spacing of about 1.In a preferred embodiment, 60 latitude rings are utilized. The diametersof the electrical contact points T, N and E are generally equal to thewidth between the latitude rings 110 so that the same contact point cannever contact more than one latitude ring.

FIG. 6 schematically illustrates the connection of the terminals ofresistor 102, 104 and 106 within the sphere 90 to a supply of positivevoltage fed through the pivot member 92 to bearing 97. The otherterminal of resistor 102 is connected to point T, which in the exampleillustrated is shown as contacting the sixth latitude ring from thecenter of the member 82. The other terminal of resistor 104 is connectedto point N, which in the example shown is also clamped on the sixthlatitude ring. The terminal of resistor 106 is connected to point E, andin the present example is shown clamped upon the l4th latitude ring fromthe center of member 82.

The particular latitude rings 110 which are in contact with points T, Nand E are sensed by the electrical scanning circuitry of the invention,in a manner to be subsequently described, which generates signalsrepresentative of the relative position of the compass sphere 90. In thepreferred method, the scanning device initiates operation with thecenter point C which represents zero angle of drift. In a stepwisemanner, the scanning device periodically scans successive latitude rings110 until a short circuit is detected between ground, the appropriatelatitude ring 110, one of the contact points T, N or E, one of theresistances 102-106 and the bearing 97. Whenever such a short circuit isdetected, the system measures the total resistivity of the circuit todistinguish between the three contact points T, N and E. The differencein resistivity is caused by the difference in magnitude of the resistors102, 104 and 106. The information obtained from the magnitude of theresistances controls the sequence in which the information istelemetered to the surface. The signals generated by the scanning deviceoperate the valve 46 in order to cause pressure pulses through thedrilling mud which are sensed uphole.

The preferred technique for telemetering information uphole isillustrated in FIG. 5. A telemetering cycle is initiated by thegeneration of a pressure pulse 120 which is received uphole and recordedon the recording chart as shown in FIG. 5. The downhole device thenscans successively at l-second intervals, and in l steps, the latituderings of the device until the scanning device senses a short circuitwith a total resistivity approximating the resistor 102. When thisresistivity is sensed, the particular latitude ring in contact withpoint T has been sensed and the pressure pulsation valve 46 is actuatedto send the pressure pulse 122 uphole for recording on the recorderchart.

The scanning device then instantaneously returns to its zero positionand is reset to detect a total resistance in a short circuit equalgenerally to resistance 104. Once the latitude ring is sensed which isin contact with contact point N, a pressure spike 124 is generated andis recorded uphole on the recorder chart. The sensing device then againreturns to its starting position at zero latitude and initiates scanningfor a short circuit having a resistivity approximating the value of theresistor 106 to determine the position of the contact point E. Upon thedetermining of the particular latitude ring 110 contacting point E, thepressure pulse 126 is generated and received uphole. The normalfluctuations of valve 46 are illustrated by the pulses 128.

After reception of a full cycle of pressure pulses in the manner shownin FIG. 5, it may often be desirable to initiate several repeatedscanning cycles so that good average measurements may be obtained.

The pressure spikes in a scanning cycle always arrive at the surface ina sequence representing the latitudes of points T, N and E. Since theangular distances between points T, N and E are known to be 30 each, andsince the three time intervals determined by the pressure spikesrepresent the latitudes measured for points T, N and E, the problem ofdetermining the angle of the drift and the direction of the drift of theborehole is now fully defined.

It will of course be understood that FIG. 6 illustrates schematicallyonly one possible particular position of the compass sphere 90, and thatother angles of inclination and directions of deviation will cause thecontact points T, N and E to contact different latitude rings.

As an example of the operation of the present device, assume that thetime interval between pressure spikes and 122 in FIG. 5 is 19 seconds,the time interval between spikes I22 and 124 is 47 seconds and the timeinterval between pressure spikes 124 nd 126 is 42 seconds. Since thespacing between the latitude rings 110 is 1, and one latitude ring issensed each second by the scanning device, the angle of the hole driftis the angular distance between point C and contact point T and is thus19".

Also, the angular distance between points C and N are equal to 47, whilethe angular distance between points N and T is equal to 30. Consideringthe triangle CNT, it may be shown by utilization of conventionalspherical trigonometric functions as defined on page 347 of C.R.C.Standard Mathematical Tables, I 954 ed., that:

z CT+ 4 C'N-l- ANT 19+47+30 T 2 2 and NT represent the latitudereadings;

r=+ sin (48-19) sin 48-47) sin (48-30) sin 48 wherein r=distance inspherical coordinates wherein x=direction of hole drift Therefore, thedirection of hole drift equals 32.7 or 327.3.

It will be seen that the above measurement results in two possiblesolutions for the direction of hole drift. In order to resolve thisambiguity, the triangle CTE is considered utilizing the sphericaltrigonometric functions defined above:

Therefore, the direction of hole drift is 28.2or l5 l.8

It is thus seen that the solutions of 327.3 and l5 1 .8 are erroneous.and that the average of the remaining two readings which are of the samemagnitude, or 30.45 is a representative value for the direction of thehole drift. The measurement of the drift of the borehole in this exampleis,

therefore, 19 N 30.45" E. For more accurate readings, a

plurality of scanning cycles are performed and the results averaged.

The foregoing calculation may be done automatically with a properlyprogrammed conventional digital computer, or with a particular specialpurpose digital computer. Alternatively, the foregoing computations maybe done by conventional analog computers or by hand.

The electronic scanning and measuring circuitry disposed in section 56of the present device will now be described in detail. FIG. 7 is a blockdiagram of the basic circuitry. The 60- wire cable 114 which containsthe wires leading from the 60 latitude rings in the constraining member82 are fed to the input of a 60-channel multiplexor 130. Multiplexor 130is sequentially stepped through each of the 60 wires to sequentiallyinterrogate each of the 60 latitude rings 110. This steppedinterrogating action is under the control ofan internal counter which istimed by a l-second clock pulse fed from an analog-to-digital converter132. i

The common terminal of the multiplexor 130 is fed to the input of theeight-level analog-to-digital converter 132. Theoutput of the converter132 senses the voltage level provided by the multiplexor 130 andgenerates digital output pulses on leads 134-138 which arerepresentative of gated voltage levels. As will later be described, theconverter 132 is operated by a l25-msec. clock output from a gated clock140 in order to step through eight trials beginning with the mostsignificant bit. Each bit value generates a voltage proportional to itsweight which is compared with the input analog voltage from themultiplexor 130. The converter generates pulses on lead 142 whichbecomes a l-second clock pulse for control of the remainder of thecircuitry.

The output of the analog-to-digital converter 132 is fed to the input ofthe control logic 144. The control logic 144 sequentially monitors theoutput leads 134-138, only moving on to monitor the next lead when anoutput pulse is received.

After receiving an output on the led being monitored, the control logiccircuit 144 emits an output pulse and moves on to monitor the nextoutput lead. The pulse emitted by the control logic circuit 144 servesto reset the multiplexor 130 via lead 146 and also to fire the solenoiddriver 148. The firing of solenoid driver 148 controls the operation ofthe pressure pulsation valve 46in order to telemeter pressure pulsesuphole in the manner previously described. The resulting output ofpressure spikes caused by operation of the valve 46 comprises threesolenoid actuations spaced apart in time, commonly termed asynchronouspulse position modulation (PPM), the time spacings being proportional tothe particular latitude rings 110 being contacted by the points T, N andE on the compass sphere 90. a 7

FIGS. -h are sample timing diagrams for portions of the operation of thecircuitry shown in FIG; 7. FIG. 8a illustrates the output from the gatedclock 40, broken down in eightcycle intervals. FIG. 8b is the power-onresetwhich initiates a scanning cycle. The remainder of the waveforms 80-11 will be explained in the description of FIGS. 9-12.

Referring to FIG. 9, the 60-wire cable 114 from the latitude rings ofthe member 82 are fed into multiplex switches 15041-11, five of whichare not shown for simplicity of illustration. In a preferred embodiment,switches l50a-li are eightchannel multiplex switches with output enablecontrol and one-out-of-eight decoder circuitry. A suitable switch foreach of the circuits l50a-h is the MOS monolithic eight-channelmultiplex switch manufactured and sold as the 3705 Integrated CircuitPackage by Fairchild Semiconductor of Mountain View, Calif.

The output from the switches 150a-h is fed via lead 152 and appearsacross theresistor 154 to the input of the analogdigital converter 132.The logic input to the switches l50a-li is controlled by the l-secondclock output of the converter 132. This clock output is fed via lead 156to the CP terminal of a three-bit binary counter comprising three J-Kflip-flop circuits 158i1-158a The clock output is also fed vial cad 156to a second three-bit binary counter comprising three J-K flip-flopcircuits l60ac. Although not shown for simplicity of illustration, the Cinputs of each of the flip-flop circuits 158a-b and 160a-c are connectedto receive the pulse solenoid signal from the control logic circuitry144 to cause each of the flipflop circuits to be DC preset.

The flip-flop circuits 158a-c and l60a c are wired as a binary counterby connecting the 6 output of each of the circuits to the .IK input ofthe adjacent flip-flopicircuit, in addition to wiring the top JK inputof each circuit to a true" level, these interconnections not shown for.simplicity of illustration. Additionally, the power voltages applied tothe circuitry are not shown for ease of illustration. Suitable circuitsfor use with the invention for the flip-flop circuit l58a-c and l60acare the "FULL 9000 J-K flip-flop circuits manufactured and sold byFairchild Semiconductor of Mountain View, Calif. The counter l58a-ckeeps track of which of the eight-channel switching circuits l50a-I1 ispresently being addressed, while the second counter 160a-c defines whichchannel within a particular switching circuit l50a-h is to be turned on.

The Q output of each of the flip-flop circuits l58ac are connected to aninput of the respective AN D-gate 164a-z, the output of which isrespectively connected through invertor circuits to an OR-gate 166a-z.The output of each of the OR- gate l66a-z are fed to the logic input ofthe switching circuits 1500-11. A number of the gates 164a-z and l66a+zhave been omitted for clarity of illustration. Suitable circuits forgates l64a-z and l66az are the TTfLL 9002 circuits sold by FairchildSemiconductor.

The Q and 6 outputs of the flip-flop circuits 1600-1 are connectedaccording to logic code to inputs of a plurality of gates 1680-12. Gates160ah comprise NOR-expansion elements, with an emitter element of eachof the elements being connected to an input of one of the AND-gates160-1. In the preferred embodiment, the NOR-expander elements 16804:

- comprise a 'ITp.L 9006 element manufactured and sold by FairchildSemiconductor of Mountain View, Calif.

The resulting output from the multiplexor circuit shown in FIG. 9 is fedvia the lead across the resistor 154 to the input of theanalog-to-digital converter 132. A bias resistor 170 is connected to asource of DC voltage at the output level. While a particular embodimentof the multiplexor has been described in detail, it will be understoodthan any suitable conventional analog multiplexor capable of handlingthe analog large input from the present device may be alternativelyutilized.

FIG. 10 illustrates the eight-level analog-to-digital converter 132wherein the analog input from multiplexor 130 is fed via lead 156 to thenegative input of high-speed differential comparator circuit 174. Thepower-on reset signal from the control logic 144 is fed to the presetinput of an analog-digital converter 176. The l-microsecond clock fromclock 140 is fed via an interface 178 to the clock input of theconverter 176 The output from the comparator 174 is fed through a diode180 to the comparator return input of the converter 176. The anode ofthe diode 180 is connected through a resistor 182 to ground. The firstreference input of the converter 176 is connected to ground, while thesecond reference input is connected to the positive bias voltage.

The analog-digital converter 176 utilizes the voltagesummingsuccessive-approximation encoder technique described in detail in thepublicatioh The Electronic Engineer, Feb. 1969, page 71. This technique,according to the present invention, provides eight possible outputlevels each spaced one thirty-second of a volt (31.25 microvolt) apart.The 125- microsecond clock steps the converter 176 through each of theeight levels beginning with the most significant bit, or hit eight. Eachof the bit values generates a voltage proportional to its weight bygating a preselected voltage into the resistor ladder network 184.Theoutput from network 184 is fed to the positive input comparator 174.If this voltage is larger than the input and log voltage appearing onlead 156, the comparator 174 determines this fact and eliminates theweight being tested. The converter 176 is then stepped to the nextsmaller weight until the level of the input and log voltage isdetermined.

After the last of the eight trials, an output pulse is generated fromthe converter 176 which is fed to an interface circuit 186 and is fed toother parts of the system as a l-second clock (see FIG 80). The biasapplied to the reference 2 input of the converter 176 adds a l/64 voltto ensure that the data at 1/32-volt intervals falls between thel/32-volt levels of the converter 176. The outputs appearing on bits 4,2 and 1 are applied via leads 188, 190 and 192 to the input of thecontrol logic circuit 144.

The comparator 174 may comprise any suitable high-speed differentialcomparator circuit, but in the preferred embodiment comprises acomparator circuit sold under the title Liner Integrated Circuits p.710by Fairchild Semiconductor of Mountain View. Calif. The ladder network184 may comprise a conventional 12.5 k0 ohm ladder network manufacturedand sold by the Negadyne Corporation of Rochester, NY. or by AngstromPrecision Inc. of Van Nuys, Calif. The converter 176 may for instancecomprise the 3751 Integrated Circuit converter manufactured and sold byFairchild Semiconductor of Mountain View, Calif. The interface elements178 and 186 are utilized to interface between the integrated circuitryand the MOS FET circuitry and may for instance comprise the 9924 and9925 Integrated Circuit Interface elements manufactured and sold byFairchild Semiconductors of Mountain View, Calif.

The eight-level sensing provided by the converter 132 is necessitated bythe possibility of multiple contacts by the contact points T, N and Ewith a single latitude ring on the member 82. The contact possibilitiesof the device of the invention are summarized by the following truthtable, wherein a l indicates a contact with a latitude ring and an 0"indicates no contact:

Parallel Resistors Combination |02(20;unhos) l04( l0) #mhos) 106(5pmhus]0 pmhos 5 umhos I 0 #mhos l5 pmhos 20 urnhos 25 pmhos 30 umhos 3S pmhosThe converter 132 thus is able to sense multiple contacts of thelatitude ring of the invention and still determine which of the contactpoints are presently being sensed. As an example, refer to FIG. 6wherein contact points T and N both contact the sixth latitude ring. Inthis case, resistors 102 and 104 are in parallel and will be gated whenthe converter 132 is in its sixth position. Assuming that resistor 102equals 50K and resistor 104 equals K, the parallel combination of theresistances is 30'umhos. the bias resistor 170 of the multiplexor addsanother 2.5 #mhos.

The particular values of the resistances 102-106 and may of course bevaried for different applications, but in this case have been chosen tomake the series resistance of the contacts and the multiplexor 130negligible. With most of the voltage applied across resistor 170 droppedacross the contact and biasresistors, the resistors act like a32.5-microamp current source into the sensing resistor 154 of themultiplexor 130. As a result, l3.64 volts, or 208.65 microvolts appearsacross resistor 154. Of this, one-eighth volt is due to resistor 102,one-sixteenth volt is due to resistor 104 and one sixtyfourth volt isdue to the bias voltage. The converter 132 senses this voltage toprovide an indication according to the truth table that contact points Tand N are in contact with the same sixth-latitude ring.

The control logic circuit 144 comprises a .l-K flip-flop circuit whichreceives as an input the l25-microsecond clock from the gated clock 140.Bias voltage is applied to the J-K inputs of the flip flop 200 through aresistor 202 and a capacitor 204. The resistor 202 and capacitor 204 actas an R-C timing network on the DC reset line of the flipflop circuit200. Once the capacitor 204 charges to above l.7 voltage, the flip-flop200 will be switched synchronously by the next I25- microsecond clockpulse. This conditioning operation should take about 25 microseconds The(5 output of the flip-flop circuit 202 acts as the power-on reset (FIG.8b) which is fed to the remainder of the circuitry as previouslydescribed. The 6 output of flip-f1op circuit 200 is also fed to the C ofthe flipflop circuits 208 and} 10 which constitute a fully decodedbinary counter. The Q output of each of the counters is connected to theJ-K input of the adjacent flip-flop circuit, with the top J-K inputwired to a true" level. In the preferred embodiment, the flip-flopcircuits 200, 208 and 210 comprise the TTpL Integrated Circuits 9000manufactured and sold by Fairchild Semiconductor of Mountain View,Calif.

The Q and Q outputs of flip-flop circuits 208 and 210 are fed to logiccircuits comprising ANDgates 214a-d and OR- gates 216d-d. In practice,the gates 214a-d and 2l6a-d may comprise ,the logic circuit manufacturedand sold as TTp.L 9002 Integrated Circuits by Fairchild Semiconductorsof Mountain View, Calif. The outputs from the gates 216a-d aredesignated P 1, (see FIG. 8e-f) and correspond to the pressure spikes120-126, shown in FIG. 5. The inputs from the converter 132 arerespectively fed to ones of AND-gates 220a-c whose outputs are connectedto an OR-gate 222. The output of the gate 222 is a pulse solenoid signal(FIG. 8d) which is fed to remaining parts of the system and is also fedto the input of the flip-flop circuit 210. The l-second clock signal isfed to an OR-gate 224 to provide clocking to the system. Gates 220ac mayfor instance comprise the integrated circuits manufactured and sold as'I'T LL 9003 and the gates 222 and 224 integrated-circuit gates sold as'I'IptL 9004 by Fairchild Semiconductor of Mountain View, Calif. Theoutputs P -P are fed to the inputs of gates 220ac to provide anindication of whether or not the pulses have been telemetered.

The pulse solenoid signal thus occurs during the power-on reset signaland also during the following l-second clock pulses: the state P, whenthe signal 4" is found by the analogdigital converter 132; or state Pwhen the signal 2"is found by the analog-digital converter 132; or whenthe signal state P is found with the l signal found by theanalog-digital converter I32.

FIG. 12 illustrates the solenoid driver 148, with the pulse solenoidsignal being fed to a pretriggerable monostable multivibrator 230.Multivibrator 230 provides an output pulse with high accuracy and with avery wide duration range in de pendence upon the level of the DC imput.In the particular configuration, multivibrator 230 is adjusted by an R-Cnetwork 232 to provide a 360-millisecond pulse (timed from the trailingedge of the pulse solenoid signal) via lead 234. The one-shot pulse fromthe monostable multivibrator 230 is fed to the solenoid driver circuit236, which may for instance comprise a high-voltage, high-currentdriver. In the preferred embodiment, the multivibrator 230 comprises theretriggefable monostable multivibrator manufactured and sold asMultivibrator T'IuL 9601 by Fairchild Semiconductor of Mountain View,Calif. while the driver 236 comprises the high-voltage, high-currentdriver SHZOOI manufactured and sold by Fairchild Semiconductor ofMountain View, Calif.

The output from the driver 236 operates the pressure valve 46 in themanner previously described, in order to control the transmission ofpressure uphole for reception, detection and recording. Once recorded,the intervals between the pressure pulses are determined to determinethe hole drift as previously noted.

Further explanation of the operation of the present circuit ingenerating two pulses may be illustrated by FIGS. 8a-h. The power-onreset causes generation of a pulse solenoid signal as shown in FIG. 8d.The l-second clock pulses shown in FIGS. 8c occur during every eighthclock pulse, as shown in FIG. 8a. Additionally, the pulse solenoidsignal shown in FIG. 8d occurs when state P is found with state 4, inthe manner previously described. Additional pulses will be generated instate P when 2" is found, or when P is found with l." The solenoid timeshown in FIG. 8h is actuated by the trailing edge of the pulse signalshown in FIG. 8d.

It will be seen that other types of position-determining apparatus maybe alternatively utilized in the present invention in place of theelectrical contact circuitry described. For instance, a light beam maybe focused upon a plurality of photoelectric cells which are disposed onthe concave side of the clamping member 82. Moreover, otherconfigurations of electrical contact points according to the inventionmay be utilized in place of the particularly specified configuration.For example, a measurement of the magnetic longitude may also beprovided according to the invention in addition to the measurement oflatitude.

The present invention thus provides an improved directional surveyingsystem compared to conventional procedures, by obtaining individualmeasurements at higher frequencies without a loss of drilling time. Theuse of a magnetic measuring device which is maintained in a frozen orconstrained position while drilling, and in an unrestrained or freeposition when circulation has stopped, makes it possible to makeaccurate measurements when the drill pipe is standing still, thereby notinvolving any loss in drilling time. The receipt of the signals from thebottom of the borehole after circulation has resumed is easily andefiiciently done with a time-driven pressure recorder which registersthe output pressure of the mud pumps.

The pressure recorder may be started at the same time that the mudcirculation is resumed after making a drill pipe connection, and therecorder may be stopped when the required number of pulse cycles andtime intervals between the cycles has been recorded. Additionally, if atany time during the drilling operations, it is desired to verify theangle and direction of the borehole drift, it is necessary only to stoprotation and circulation, wait the required short interval and resumecirculation and rotation. As previously noted, systems may be providedwhich automatically calculate and plot the angle and direction of theborehole from the transmitted pressure pulses.

Whereas the present invention has been described with respect to aspecific embodiment thereof, it will be understood that various changesand modifications may become apparent to one skilled in the art, and itis intended to encompass those changes and modifications as fall withinthe scope of the appended claims.

I claim:

I. In a drill system, the combination comprising:

a. structure defining a chamber in the region of the drill bit of saiddrill system,

b. reference means movable within said chamber and including structurefor maintaining said reference means in a preselected orientation withrespect to magnetic north,

c. means responsive to mudflow of said drill system for clamping saidreference means in position, and

d. means disposed in the region of said drill bit for detecting therelative positions of said reference means and said drill bit while saidreference means is clamped.

2. The combination of claim I and further comprising:

means for telemetering indications uphole of the relative positions ofsaid reference means and said drill bit to define the inclination anddirection of said drill system.

3. The combination of claim 2 wherein said means for telemeteringcomprises mud-valve means, and means for modulating said mud-valve meansin accordance with the relative positions of said reference means andsaid drill bit.

4. The combination of claim 1 wherein said reference means comprises agenerally spherical member with a magnetic element embedded therein andincludes means to maintain said member within a preselected region ofmovement.

5. The combination of claim 4 wherein said reference means is suspendedin quantity of liquid contained within said chamber.

6. The combination of claim 4 wherein said reference means includes acutout portion within which a pin member rigidly suspended from saiddrill system is pivotally connected.

7. The combination of claim 6 wherein said cutout portion is generallyconical, with the end of said pin member pivotally connected at the apexof the cutout portion.

8. The combination of claim 4 and further comprising:

a clamping member having a spherical cutout portion adapted to receivesaid spherical member and operable in response to changes in mudflow ofsaid drill system for selectively abutting said spherical member in aclamping relationship.

9. The combination of claim 8 wherein said spherical member comprises:

A plurality of electrical conductive points thereon, said clampingmember including a plurality of means for sensing the position of saidelectrically conductive points.

10. A system for surveying the drift of a directional drill comprising:

a generally spherical reference member adapted to move about a pivotrelative to said drill to seek a reference orientation within saiddrill,

means for maintaining said reference member in a stationary positionwithin said drill during drilling operations,

means for releasing said reference member in response to temporarycessation of drilling operations to enable said reference member to moverelative to said drill to seek said reference orientation, and

means operable during drilling operations for detecting the relativeposition of said reference member with respect to said drill.

I l. The system of claim I0 and further comprising:

clamping means slidable within said drill and having a portion adaptedto abut against said spherical reference member for maintaining saidreference member in a stationary position within said drill,

port means disposed uphole and downhole from said reference member forsensing variances in the mud pressure flowing through said drill, and

bellows means connected to said port means for selectively moving saidclamping means into and out of engagement with said spherical referencemember in response to variances in the mud pressure.

12. The system of claim wherein said spherical reference member includesthree conductive portions on the exterior thereof, one of saidconductive portions being disposed on the upper portion of saidreference member and the remaining two conductive portions beingdisposed along lines intersecting at a right angle at said firstconductive portion.

13. The system of claim 12 and further comprising:

a plurality of rings disposed on said clamping means for sensing theposition of said conductive portions on said spherical reference member.

14. The system of claim 10 wherein said generally spherical referencemember includes a generally conical cutout portion in the lower portionthereof,

a pin member rigidly connected at one end to said drill and extendinginto the conical-shaped cutout portion and attached at the apex thereoffor pivotally supporting said spherical reference member.

15. The method of surveying the inclination of a directional drillcomprising:

maintaining a reference member in a stationary position within saiddrill during drilling operations,

releasing said reference member in response to temporary cessation ofdrilling operations such that said reference member seeks apredetermined reference orientation relative to magnetic north,

clamping in response to resumption of drilling operations said referencemember in a stationary position after said reference member has reachedits predetermined reference orientation, and

detecting during drilling operations the relative position of said drillwith respect to said reference member while said reference member isclamped in a stationary position.

16. The method of claim 15 wherein said reference member seeks saidpredetermined reference orientation due to the attraction of the earthsambient magnetic and gravitational fields.

17. The method of claim 16 wherein said step of detecting comprises:

detecting the position of at least three conductive portions on saidreference member, and

distinguishing each of said conductive portions from one another bymeasuring the electrical resistance provided by said conductiveportions.

18. The method of claim 16 and further comprising:

telemetering the detected relative positions of said drill with respectto said reference member uphole during drilling operations by impartingcoded pulsations into the drilling mud of the drill system.

19. The method of claim 16 and further comprising:

monitoring the variance in the mud pressure of said drill caused byinitiation and cessation of drilling operations, and

controlling the state of freedom of said reference member in response tovariances in the mud pressure.

20. In a directional directional detection system for a drill.

the combination comprising:

a generally spherical reference member having a magnet embedded thereinfor seeking a reference orientation within said drill due to theattraction of the ambient magnetic field of the earth,

said reference member including a plurality of conductive pointsdistributed on the exterior surface thereof,

resistance means connected to each of said conductive points, and

means including a plurality of concentric conductive rings forcontacting said conductive oints to detect the ositron of saidconductive points y measurements 0 the magnitude of said resistances.

21. The combination of claim 20 and wherein said means for detectingcomprises:

a member having a concave portion adapted to receive a portion of saidspherical reference member and including said conductive rings thereonfor contacting said conductive points on said spherical referencemember.

22. The combination of claim 21 wherein said conductive points on saidspherical reference member comprise:

a first point position at he uppermost point of said spherical memberand including second and third conductive points dispose along linesintersecting at a right angle at said first point position.

23. The combination of claim 21 and further comprising:

multiplexer means for generating analog signals representative of theconductive rings which are in contact with said conductive points,

means for converting said analog signals into digital signals,

and

means responsive to said digital signals for generating control signals.

24. The combination of claim 23 and further comprising:

mud valve means operable in response to said control signals fortransmitting mud pulses uphole representative of the position of saidreference member.

"H050 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,622,971 Dated Nov 23, 1971 lnven fl Jan J. Arlis It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

C ol 6-, line 59 "nd" should be and-. 1

Col 7, line 1, "sin( 48-l9)sin t8 l7)sin( 48-30) in the equation shouldbe sin( l8-l9)sin(U8- l7),sin( l8-3O). Col 8, line 17, "clock 40" shouldbe -,-v--olo1ck lUO-;

line 72, "1661-2" should be -l6 4aZ. Col. 9, line 2, "lead 15" should belead 152--;

line 52 "Liner" should be --Linear-; lin 53, "p710" should be --uA7lO;line 55, "12.5 k Qohm" should be l2 .5 k ohm--. Col 10, line 1, above"Combination" insert Paralleland above "lO l(lOun1hos)" insertResistors-; line 6, in 4th column insert --O--. Col 11, line 13, "imput"should be -input-. Col 12, line 37, before "quantity" insert --a. Col 1line 12, cancel "directional" (first occurrence) line 3Q, "he" should be-the-; line 36, "dispose" should be --disposed- Signed and sealed this20th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCI-ER, JR. ROBERT GOTTSCHALK Attesting Officer Co missionerof Patents

1. In a drill system, the combination comprising: a. structure defininga chamber in the region of the drill bit of said drill system, b.reference means movable within said chamber and including structure formaintaining said reference means in a preselected orientation withrespect to magnetic north, c. means responsive to mudflow of said drillsystem for clamping said reference means in position, and d. meansdisposed in the region of said drill bit for detecting the relativepositIons of said reference means and said drill bit while saidreference means is clamped.
 2. The combination of claim 1 and furthercomprising: means for telemetering indications uphole of the relativepositions of said reference means and said drill bit to define theinclination and direction of said drill system.
 3. The combination ofclaim 2 wherein said means for telemetering comprises mud-valve means,and means for modulating said mud-valve means in accordance with therelative positions of said reference means and said drill bit.
 4. Thecombination of claim 1 wherein said reference means comprises agenerally spherical member with a magnetic element embedded therein andincludes means to maintain said member within a preselected region ofmovement.
 5. The combination of claim 4 wherein said reference means issuspended in quantity of liquid contained within said chamber.
 6. Thecombination of claim 4 wherein said reference means includes a cutoutportion within which a pin member rigidly suspended from said drillsystem is pivotally connected.
 7. The combination of claim 6 whereinsaid cutout portion is generally conical, with the end of said pinmember pivotally connected at the apex of the cutout portion.
 8. Thecombination of claim 4 and further comprising: a clamping member havinga spherical cutout portion adapted to receive said spherical member andoperable in response to changes in mudflow of said drill system forselectively abutting said spherical member in a clamping relationship.9. The combination of claim 8 wherein said spherical member comprises: Aplurality of electrical conductive points thereon, said clamping memberincluding a plurality of means for sensing the position of saidelectrically conductive points.
 10. A system for surveying the drift ofa directional drill comprising: a generally spherical reference memberadapted to move about a pivot relative to said drill to seek a referenceorientation within said drill, means for maintaining said referencemember in a stationary position within said drill during drillingoperations, means for releasing said reference member in response totemporary cessation of drilling operations to enable said referencemember to move relative to said drill to seek said referenceorientation, and means operable during drilling operations for detectingthe relative position of said reference member with respect to saiddrill.
 11. The system of claim 10 and further comprising: clamping meansslidable within said drill and having a portion adapted to abut againstsaid spherical reference member for maintaining said reference member ina stationary position within said drill, port means disposed uphole anddownhole from said reference member for sensing variances in the mudpressure flowing through said drill, and bellows means connected to saidport means for selectively moving said clamping means into and out ofengagement with said spherical reference member in response to variancesin the mud pressure.
 12. The system of claim 10 wherein said sphericalreference member includes three conductive portions on the exteriorthereof, one of said conductive portions being disposed on the upperportion of said reference member and the remaining two conductiveportions being disposed along lines intersecting at a right angle atsaid first conductive portion.
 13. The system of claim 12 and furthercomprising: a plurality of rings disposed on said clamping means forsensing the position of said conductive portions on said sphericalreference member.
 14. The system of claim 10 wherein said generallyspherical reference member includes a generally conical cutout portionin the lower portion thereof, a pin member rigidly connected at one endto said drill and extending into the conical-shaped cutout portion andattached at the apex thereof for pivotally supporting said sphericalreference member.
 15. The method of surveying The inclination of adirectional drill comprising: maintaining a reference member in astationary position within said drill during drilling operations,releasing said reference member in response to temporary cessation ofdrilling operations such that said reference member seeks apredetermined reference orientation relative to magnetic north, clampingin response to resumption of drilling operations said reference memberin a stationary position after said reference member has reached itspredetermined reference orientation, and detecting during drillingoperations the relative position of said drill with respect to saidreference member while said reference member is clamped in a stationaryposition.
 16. The method of claim 15 wherein said reference member seekssaid predetermined reference orientation due to the attraction of theearth''s ambient magnetic and gravitational fields.
 17. The method ofclaim 16 wherein said step of detecting comprises: detecting theposition of at least three conductive portions on said reference member,and distinguishing each of said conductive portions from one another bymeasuring the electrical resistance provided by said conductiveportions.
 18. The method of claim 16 and further comprising:telemetering the detected relative positions of said drill with respectto said reference member uphole during drilling operations by impartingcoded pulsations into the drilling mud of the drill system.
 19. Themethod of claim 16 and further comprising: monitoring the variance inthe mud pressure of said drill caused by initiation and cessation ofdrilling operations, and controlling the state of freedom of saidreference member in response to variances in the mud pressure.
 20. In adirectional directional detection system for a drill, the combinationcomprising: a generally spherical reference member having a magnetembedded therein for seeking a reference orientation within said drilldue to the attraction of the ambient magnetic field of the earth, saidreference member including a plurality of conductive points distributedon the exterior surface thereof, resistance means connected to each ofsaid conductive points, and means including a plurality of concentricconductive rings for contacting said conductive points to detect theposition of said conductive points by measurements of the magnitude ofsaid resistances.
 21. The combination of claim 20 and wherein said meansfor detecting comprises: a member having a concave portion adapted toreceive a portion of said spherical reference member and including saidconductive rings thereon for contacting said conductive points on saidspherical reference member.
 22. The combination of claim 21 wherein saidconductive points on said spherical reference member comprise: a firstpoint position at he uppermost point of said spherical member andincluding second and third conductive points dispose along linesintersecting at a right angle at said first point position.
 23. Thecombination of claim 21 and further comprising: multiplexor means forgenerating analog signals representative of the conductive rings whichare in contact with said conductive points, means for converting saidanalog signals into digital signals, and means responsive to saiddigital signals for generating control signals.
 24. The combination ofclaim 23 and further comprising: mud valve means operable in response tosaid control signals for transmitting mud pulses uphole representativeof the position of said reference member.